1. Field of the Invention
The present invention relates to a method for manufacturing a transistor and a transistor.
2. Background
An organic transistor can be manufactured at low temperatures compared to an inorganic silicon thin film transistor of the related art and has advantages such as a capability of being formed onto a flexible substrate using a resin material and thereby formed into an organic transistor having flexibility or capable of being formed by a low-cost solution process which is suitable for size increase. Therefore, research has been actively conducted as the core of the next-generation flexible electronics.
The structure of an organic thin film transistor is generally classified into a bottom contact type or a top contact type. Of these two types, the bottom contact thin film transistor is obtained by forming an organic semiconductor layer onto a substrate on which a circuit pattern is formed in advance and therefore has an advantage that the organic semiconductor layer is not degraded by physical or chemical stress associated with electrode formation.
On the other hand, in the bottom contact organic thin film transistor, contact resistance (Schottky resistance) between an organic semiconductor and a metal wiring arises due to the difference between the work function of a metal material which constitutes an electrode and the HOMO (Highest Occupied Molecular Orbital) (or LUMO (Lowest Unoccupied Molecular Orbital)) level of the organic semiconductor, and therefore there is a problem in that the performance of the bottom contact organic thin film transistor is inferior to that of the top contact organic thin film transistor.
In a case where a gold wiring is formed on an insulator layer by evaporation, sputtering, or the like, a titanium layer or a chromium layer is required as an adhesive layer. Because titanium or chromium has a small work function, there is a problem in that the charge injection characteristics into an organic semiconductor such as pentacene are degraded. In order to solve this problem, D. Kumaki, Appl. Phys. Lett., 92, 013301 (2008) proposes a configuration which employs a laminate structure of a metal layer and a metal oxide layer having superior charge injection characteristics into an organic semiconductor, for source and drain electrodes such that the charge injection barrier between the electrode layer and the organic semiconductor layer is reduced.
In addition, P. Marmont et al., Organic Electronics (2008), doi: 10.1016/j.orgel. 2008.01.004 discloses a TFT of which an Au (gold) electrode is treated by SAMs (Self Assembled Monolayers) such as decanethiol (DT), perfluorodecanethiol (PFDT), or perfluorohexanethiol (PFHT) so as to change the work function and the electron injection from the electrode is improved.